Excellent Oxygen Evolution Reaction of Activated Carbon-Anchored NiO Nanotablets Prepared by Green Routes

Tuning ZnO-based piezoelectric nanogenerator efficiency through n-ZnO/p-NiO bulk interfacing

ZnO based piezoelectric nanogenerators (PENG) hold immense potential for harvesting ambient vibrational mechanical energy into electrical energy, offering sustainable solutions in the field of self-powered sensors, wearable electronics, human-machine interactions etc. In this study, we have developed flexible ZnO-based PENGs by incorporating ZnO microparticles into PDMS matrix, with ZnO concentration ranging from 5 to 25 wt%. Among these, the PENG containing 15 wt% ZnO exhibited the best performance with an open-circuit output voltage/short-circuit current of ~ 42.4 V/2.4 µA. To further enhance the output performance of PENG, p-type NiO was interfaced with ZnO in a bulk hetero-junction geometry. The concentration of NiO was varied from 5 to 20 wt% with respect to ZnO and incorporated into the PDMS matrix to fabricate the PENGs. The PENG containing 10 wt% NiO exhibits the best performance with an open-circuit output voltage/short-circuit current of ~ 65 V/4.1 µA under loading conditions of 30 N and 4 Hz. The PENG exhibiting the best performance demonstrates a maximum instantaneous output power density ~ 37.9 µW/cm2 across a load resistance of 20 MΩ under loading conditions of 30 N and 4 Hz, with a power density per unit force and Hertz of about ~ 0.32 µW/cm2·N·Hz. The enhanced output performance of the PENG is attributed to the reduction in free electron concentration, which suppresses the internal screening effect of the piezopotential. To assess the practical utility of the optimized PENG, we tested the powering capability by charging various commercial capacitors and used the stored energy to illuminate 10 LEDs and to power a stopwatch displays. This work not only presents a straightforward, cost-effective, and scalable technique for enhancing the output performance of ZnO-based PENGs but also sheds light on its underlying mechanism.

Metal oxide-embedded carbon-based materials for polymer solar cells and X-ray detectors

This study examines the effects of hybrid nanoparticles made of NiO@rGO (reduced graphene oxide) and NiO@CNT (carbon nanotubes) on PCDTBT and PCBM active layers in glass/ITO/HTL/active-layer/LiF/Al structured bulk heterojunction (BHJ) polymer solar cells (PSCs) and X-ray photodetectors. These hybrid nanoparticles were used to create BHJ solar cells and photodetectors, and microscopic research was conducted to determine how they affect the structure of the devices. The findings show that compared to conventional matrices, the active layers with NiO@rGO and NiO@CNT incorporation have increased the charge carrier capacities and exciton dissociation properties. In order to assess their impact on the characteristics of charge transport, various weight ratios of these hybrid nanoparticles dispersed in polymer junctions are being investigated. Notably, compared to the pure PCDTBT:PCBM active layer (power conversion efficiency (PCE) = 4.35%), the NiO@CNT device has the highest PCE = 6.42% which, among the tested configurations, demonstrates its superior performance in converting sunlight into electricity. Among the tested X-ray detector materials, "NiO@CNT" achieves the best performance with a sensitivity of 1.92 mA Gy-1 cm-2. Through improved interfacial behaviors and effective charge transport, this work highlights the potential of these cutting-edge hybrid nanoparticles to enhance the performance of organic electronic devices.

Waste-Derived Catalysts for Water Electrolysis: Circular Economy-Driven Sustainable Green Hydrogen Energy

The sustainable production of green hydrogen via water electrolysis necessitates cost-effective electrocatalysts. By following the circular economy principle, the utilization of waste-derived catalysts significantly promotes the sustainable development of green hydrogen energy. Currently, diverse waste-derived catalysts have exhibited excellent catalytic performance toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water electrolysis (OWE). Herein, we systematically examine recent achievements in waste-derived electrocatalysts for water electrolysis. The general principles of water electrolysis and design principles of efficient electrocatalysts are discussed, followed by the illustration of current strategies for transforming wastes into electrocatalysts. Then, applications of waste-derived catalysts (i.e., carbon-based catalysts, transitional metal-based catalysts, and carbon-based heterostructure catalysts) in HER, OER, and OWE are reviewed successively. An emphasis is put on correlating the catalysts' structure-performance relationship. Also, challenges and research directions in this booming field are finally highlighted. This review would provide useful insights into the design, synthesis, and applications of waste-derived electrocatalysts, and thus accelerate the development of the circular economy-driven green hydrogen energy scheme.

Enhanced photocatalytic crystal-violet degradation performances of sonochemically-synthesized AC-CeO2 nanocomposites

Semiconductor-based photocatalysis is one of the favorable techniques for the wastewater treatment. Herein, we synthesized the activated carbon-decorated cerium dioxide (AC-CeO₂) nanocomposites via the facile ultrasonication method by using the biomass-derived AC nanoflakes and the sonochemically-synthesized CeO₂ nanoparticles. The AC-CeO₂ nanocomposites exhibited the aggregated morphology with the AC nanoflakes-anchored CeO₂ nanoparticles. Since the hybridization of conductive AC and semiconductive CeO₂ would lead to the increased photocarrier transport and the reduced photocarrier recombination, during the photocatalytic reaction, the AC-CeO₂ nanocomposites showed the enhanced crystal violet dye-degradation efficiency up to 97.9 % within 135 min. The results suggest that the AC-CeO₂ nanocomposites hold promise as a prominent photocatalyst for future green environmental technology.

Excellent Electrocatalytic Hydrogen Evolution Reaction Performances of Partially Graphitized Activated-Carbon Nanobundles Derived from Biomass Human Hair Wastes

Carbonaceous materials play a vital role as an appropriate catalyst for electrocatalytic hydrogen production. Aiming at realizing the highly efficient hydrogen evolution reaction (HER), the partially graphitized activated-carbon nanobundles were synthesized as a high-performance HER electrocatalyst by using biomass human hair ashes through the high-temperature KOH activation at two different temperatures of 600 and 700 °C. Due to the partial graphitization, the 700 °C KOH-activated partially graphitized activated-carbon nanobundles exhibited higher electrical conductivity as well as higher textural porosity than those of the amorphous activated-carbon nanobundles that had been prepared by the KOH activation at 600 °C. As a consequence, the 700 °C-activated partially graphitized activated-carbon nanobundles showed the extraordinarily high HER activity with the very low overpotential (≈16 mV at 10 mA/cm² in 0.5 M H₂SO₄) and the small Tafel slope (≈51 mV/dec). These results suggest that the human hair-derived partially graphitized activated-carbon nanobundles can be effectively utilized as a high-performance HER electrocatalyst in future hydrogen-energy technology.

Excellent photocatalytic performances of Co3O4-AC nanocomposites for H2 production via wastewater splitting

Natural sunlight-driven photocatalytic hydrogen production from wastewater is one of the most desirable techniques that can realize future green energy technology. Herein, we report the synthesis and the characterization of the biomass activated carbon (AC)-decorated cobalt oxide (Co₃O₄) nanocomposites for solar-stimulated photocatalytic hydrogen production from sulphide wastewater. The Co₃O₄-AC nanocomposites were ultrasonically synthesized by using hydrothermally-grown spinel Co₃O₄ nanoflakes and biomass-derived AC nanoflakes. Co₃O₄-AC showed a nanobundle-like aggregated morphology, and exhibited a large specific surface area (~133 m²/g). Through utilizing Co₃O₄-AC as a photocatalyst for photocatalytic splitting of sulphide wastewater (0.2 M) under solar irradiance with 730 W/m², an enhanced H₂ production efficiency (~70 mL/h) was achieved owing to the synergic effects from 2-dimentionally configured Co₃O₄ and AC microstructures; i.e., large surface area of Co₃O₄ and high electrical conductivity of AC. These findings suggest the nanocomposites of Co₃O₄-AC to hold great promise for the green approach of photocatalytic wastewater splitting.

TriMOF synergized on the surface of activated carbon produced from pineapple leaves for the environmental pollutant reduction and oxygen evolution process

Facile and modest synthesis of significantly effective and less-cost catalysts for environmental pollutant degradation and oxygen evolution holds substantial potential in environmental and energy fields. Hereby, Trimetallic organic frameworks (TriMOF) consisting of Fe, Co, and Zn synergized on the surface of activated carbon (AC) from pineapple leaves tend to show exponential catalytic activity due to the more excellent ionic conductivity, catalytic stability and multiple active sites provided by different metal precursors. Furthermore, the developed nanocomposite was coated on the stainless-steel electrode substrate at room temperature, delivering greater electrocatalytic surface area and numerous active sites. The oxidation reaction kinetics drives the catalytic reduction of 4-nitrophenol to 4-aminophenol with a minimal time of 12 min @ >97 % efficiency. Furthermore, on electrocatalytic oxidation of water splitting process due to the presence of multiple metallic, active sites, the overpotential is at 370 mV having Tafel slope of 40 mV/dec and electrochemically active surface area of is 9.9 mF/cm². This superior catalytic reduction of 4-nitrophenol and electrocatalytic water oxidation process is attributed to the developed composite's active centre and conductivity.

Phytochemical-Assisted Green Synthesis of Nickel Oxide Nanoparticles for Application as Electrocatalysts in Oxygen Evolution Reaction

Electrocatalytic water splitting is a promising solution to resolve the global energy crisis. Tuning the morphology and particle size is a crucial aspect in designing a highly efficient nanomaterials-based electrocatalyst for water splitting. Herein, green synthesis of nickel oxide nanoparticles using phytochemicals from three different sources was employed to synthesize nickel oxide nanoparticles (NiOx NPs). Nickel (II) acetate tetrahydrate was reacted in presence of aloe vera leaves extract, papaya peel extract and dragon fruit peel extract, respectively, and the physicochemical properties of the biosynthesized NPs were compared to sodium hydroxide (NaOH)-mediated NiOx. Based on the average particle size calculation from Scherrer’s equation, using X-ray diffractograms and field-emission scanning electron microscope analysis revealed that all three biosynthesized NiOx NPs have smaller particle size than that synthesized using the base. Aloe-vera-mediated NiOx NPs exhibited the best electrocatalytic performance with an overpotential of 413 mV at 10 mA cm−2 and a Tafel slope of 95 mV dec−1. Electrochemical surface area (ECSA) measurement and electrochemical impedance spectroscopic analysis verified that the high surface area, efficient charge-transfer kinetics and higher conductivity of aloe-vera-mediated NiOx NPs contribute to its low overpotential values.

Optimization of Oxygen Evolution Reaction with Electroless Deposited Ni-P Catalytic Nanocoating

The low efficiency of water electrolysis mostly arises from the thermodynamic uphill oxygen evolution reaction. The efficiency can be greatly improved by rationally designing low-cost and efficient oxygen evolution anode materials. Herein, we report the synthesis of Ni-P alloys adopting a facile electroless plating method under mild conditions on nickel substrates. The relationship between the Ni-P properties and catalytic activity allowed us to define the best conditions for the electroless synthesis of highperformance Ni-P catalysts. Indeed, the electrochemical investigations indicated an increased catalytic response by reducing the thickness and Ni/P ratio in the alloy. Furthermore, the Ni-P catalysts with optimized size and composition deposited on Ni foam exposed more active sites for the oxygen evolution reaction, yielding a current density of 10 mA cm-2 at an overpotential as low as 335 mV, exhibiting charge transfer resistances of only a few ohms and a remarkable turnover frequency (TOF) value of 0.62 s-1 at 350 mV. The present study provides an advancement in the control of the electroless synthetic approach for the design and large-scale application of high-performance metal phosphide catalysts for electrochemical water splitting.

3D porous Ni/NiOx as a bifunctional oxygen electrocatalyst derived from freeze-dried Ni(OH)2

Bifunctional electrocatalytic properties of freeze-dried Ni/NiOx, freeze-dried NiO, and freeze-dried Ni(OH)2 are reported. Freeze-dried Ni(OH)2 was synthesized by the freeze-drying method. Freeze-dried Ni/NiOx and freeze-dried Ni were obtained from the thermal annealing of the material. Both Ni(OH)2 and Ni/NiOx could sustain with freestanding freeze-dried 3D structures without any carbon support. Freeze-dried Ni/NiOx exhibited excellent bifunctional electrocatalytic properties with the ORR performance at 0.62 V (half-wave potential) and OER at 1.47 V (η = 10 mA cm-2). Using freeze-dried metal hydroxides can be considered useful in a wide range of carbon-free applications and can improve the electrocatalytic performance. The bifunctional catalytic activities were calculated to be 0.86, 0.98 and 1.14 V for freeze-dried Ni/NiOx, freeze-dried NiO and freeze-dried Ni(OH)2, respectively. The stacking of 2D sheets into 3D mass seemed to play a vital role behind this excellent bifunctionality of freeze-dried Ni/NiOx. The material reveals possible applications in Zn-air batteries. Besides, the strategy developed herein could be justified to obtain other transition metal-oriented bifunctional electrocatalysts as alternatives to Pt- and Ir/Ru-based expensive benchmark catalysts.

One-Pot Synthesized Biomass C-Si Nanocomposites as an Anodic Material for High-Performance Sodium-Ion Battery

Aiming at materializing an excellent anodic source material of the high-performance sodium-ion battery (SIB), we fabricated the biomass carbon-silicon (C-Si) nanocomposites by the one-pot synthesis of facile magnesiothermic reduction using brown rice husk ashes. The C-Si nanocomposites displayed an aggregated morphology, where the spherical Si nanoparticles (9 nm on average) and the C nanoflakes were encapsulated and decorated with each other. When utilizing the nanocomposites as an SIB anode, a high initial discharge capacity (i.e., 378 mAh/g at 100 mA/g) and a high reversible capacity (i.e., 122 mAh/g at 200 mA/g) were achieved owing to their enhanced electronic and ionic conductivities. Moreover, the SIB device exhibited a high cyclic stability in its Coulombic efficiency (i.e., 98% after 100 charge-discharge cycles at 200 mA/g). These outstanding results depict that the one-pot synthesized biomass C-Si nanocomposites are beneficial for future green energy-storage technology.

Upcycling of Wastewater via Effective Photocatalytic Hydrogen Production Using MnO2 Nanoparticles-Decorated Activated Carbon Nanoflakes

In the present work, we demonstrated the upcycling technique of effective wastewater treatment via photocatalytic hydrogen production by using the nanocomposites of manganese oxide-decorated activated carbon (MnO₂-AC). The nanocomposites were sonochemically synthesized in pure water by utilizing MnO₂ nanoparticles and AC nanoflakes that had been prepared through green routes using the extracts of Brassica oleracea and Azadirachta indica, respectively. MnO₂-AC nanocomposites were confirmed to exist in the form of nanopebbles with a high specific surface area of ~109 m²/g. When using the MnO₂-AC nanocomposites as a photocatalyst for the wastewater treatment, they exhibited highly efficient hydrogen production activity. Namely, the high hydrogen production rate (395 mL/h) was achieved when splitting the synthetic sulphide effluent (S²⁻ = 0.2 M) via the photocatalytic reaction by using MnO₂-AC. The results stand for the excellent energy-conversion capability of the MnO₂-AC nanocomposites, particularly, for photocatalytic splitting of hydrogen from sulphide wastewater.